The present invention relates to the manufacture of apertured shapes of sheet material, and is particularly directed to a method and system for producing adhesive backed rings such as reinforcing rings for floppy disks employed in computers.
Sheet materials, such as paper and plastic sheets, is now often cut into individual shaped pieces using die cutting techniques. A rotary cylindrical or reciprocable planar die having a raised cutting outline engages the sheet material against a fixed reference surface or anvil to cut the desired outline to precise shape, usually at high speed. Where all edges can tolerate minor bending or imprecision both the outer periphery and inner apertures on the die cut part can be formed on a single pass. Where no deformation or irregularity can be permitted, however, more complex techniques have had to be used. An example is found in the manufacture of reinforcing rings for floppy or flexible disks.
Substantial and widespread use is made of floppy disks in both small and large computers. Such disks are comprised of a thin pliant magnetic material retained within an envelope having openings for receiving drive members and magnetic heads. The floppy disks themselves have a plastic, e.g. Mylar, base with magnetic material on one or both sides. Each disk includes a central hole of substantially precise dimension used in positioning the disk for rotation.
In use, the floppy disk within its envelope is placed in a disk drive mechanism where a central positioning system, including a positioning hub, engages within the central hole and centers the inner periphery of the disk in position relative to the mechanism, and then rotates it. Because data on the disk is recorded in narrow closely spaced tracks, any disk eccentricity arising from inaccurate positioning can increase the possibility of data error. Because the disk must be shifted within its envelope and because repeated use causes wear and distortion of the inner periphery, accurate and repeatable positioning is not reliably achieved. To overcome or at least reduce such problems, suppliers and users often place a reinforcing ring around the disk, such ring being an adhesive-backed plastic material which reinforces the center of the disk and enables it to be positioned more precisely in the mechanism as well as to have a longer life.
The rings are generally formed from a strip or sheet of thin compliant material, such as a vinyl sheet, which is removably affixed by an adhesive to a paper backing. High speed die cutting is used to form the rings from the sandwich material. The rings may be formed by a double level cutting die, rotary or reciprocating, which cuts the center hole through the vinyl and the backing, but forms the outer radius by cutting only through the vinyl. This leaves the ring on the backing strip for subsequent application by machine to a disk. It is much more difficult, however, to fabricate and maintain a precise double level die than a single level die. Also, in making a full cut through the sandwich to form the rings, the inner periphery is heavily stressed and may be deformed. Additionally, the silicone adhesive which attaches the pliant sheet to the paper backing exudes and causes distortion at the edges. These irregularities adversely affect the precision with which the floppy disk can be positioned and may render the disk unacceptable.
This fabrication of precisely shaped reinforcing rings so as to leave the rings on a backing for subsequent mounting on floppy disks is a particularly high volume illustration of one application of techniques in accordance with the invention. It often happens that precisely formed or intricately shaped elements of sheet material are to be formed at high speed and low cost without damaging the peripheries of interior surface apertures.
It is accordingly one object of the invention to provide a simple method and system for forming precise apertured shapes in sheet members at realistic production rates using die cutting techniques.
Another object is the provision of a method and system for accurately cutting apertured shapes from a sandwich comprising a pliant sheet material affixed by a detachable adhesive to a backing sheet.
Yet another object of the invention is to provide procedure and apparatus for cutting shapes from a sheet material on a backing strip under conditions to prevent the adhesive from exuding from beneath the shape and without causing distortion at the edges of the shape.